Pieces protecting king

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 62620a77bad7f0ef0b4add0e073c099c6a478249..84c832695dee5d3a43234c9045541b0f30009534 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -180,6 +180,16 @@ namespace {
     S(  9, 10), S( 2, 10), S( 1, -8), S(-20,-12),
     S(-20,-12), S( 1, -8), S( 2, 10), S(  9, 10)
   };
+  
+  // Protector[PieceType][distance] contains a protecting bonus for our king, 
+  // indexed by piece type and distance between the piece and the king.
+  const Score Protector[PIECE_TYPE_NB][8] = {
+  {}, {},
+    { S(0, 0), S( 7, 9), S( 7, 1), S( 1, 5), S(-10,-4), S( -1,-4), S( -7,-3), S(-16,-10) }, // Knight
+    { S(0, 0), S(11, 8), S(-7,-1), S(-1,-2), S( -1,-7), S(-11,-3), S( -9,-1), S(-16, -1) }, // Bishop
+    { S(0, 0), S(10, 0), S(-2, 2), S(-5, 4), S( -6, 2), S(-14,-3), S( -2,-9), S(-12, -7) }, // Rook
+    { S(0, 0), S( 3,-5), S( 2,-5), S(-4, 0), S( -9,-6),  S(-4, 7), S(-13,-7), S(-10, -7) }  // Queen
+  };
 
   // Assorted bonuses and penalties used by evaluation
   const Score MinorBehindPawn     = S(16,  0);
@@ -294,6 +304,9 @@ namespace {
         int mob = popcount(b & ei.mobilityArea[Us]);
 
         mobility[Us] += MobilityBonus[Pt][mob];
+        
+        // Bonus for this piece as a king protector
+        score += Protector[Pt][distance(s, pos.square<KING>(Us))];
 
         if (Pt == BISHOP || Pt == KNIGHT)
         {
@@ -377,11 +390,12 @@ namespace {
 
   // evaluate_king() assigns bonuses and penalties to a king of a given color
 
+  const Bitboard QueenSide   = FileABB | FileBBB | FileCBB | FileDBB;
   const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
+  const Bitboard KingSide    = FileEBB | FileFBB | FileGBB | FileHBB;
 
   const Bitboard KingFlank[FILE_NB] = {
-    CenterFiles >> 2, CenterFiles >> 2, CenterFiles >> 2, CenterFiles, CenterFiles,
-    CenterFiles << 2, CenterFiles << 2, CenterFiles << 2
+    QueenSide, QueenSide, QueenSide, CenterFiles, CenterFiles, KingSide, KingSide, KingSide
   };
 
   template<Color Us, bool DoTrace>
@@ -724,14 +738,15 @@ namespace {
     int kingDistance =  distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
                       - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
     int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
+    bool bothFlanks = (pos.pieces(PAWN) & QueenSide) && (pos.pieces(PAWN) & KingSide);
 
     // Compute the initiative bonus for the attacking side
-    int initiative = 8 * (asymmetry + kingDistance - 15) + 12 * pawns;
+    int initiative = 8 * (asymmetry + kingDistance - 17) + 12 * pawns + 16 * bothFlanks;
 
     // Now apply the bonus: note that we find the attacking side by extracting
     // the sign of the endgame value, and that we carefully cap the bonus so
-    // that the endgame score will never be divided by more than two.
-    int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg / 2));
+    // that the endgame score will never change sign after the bonus.
+    int value = ((eg > 0) - (eg < 0)) * std::max(initiative, -abs(eg));
 
     return make_score(0, value);
   }